Those who are familiar with the industry will appreciate that a reverse osmosis water purification system provides for cleaning an impure aqueous solution by forcing the solution through a semi-permeable membrane to obtain a substantially pure aqueous solution. More particularly, an impure aqueous solution is generally pumped, under pressure, through the semi-permeable membrane, which is designed for retaining impurities such as organic and inorganic substances, thereby effecting passage only of the substantially pure aqueous solution through the membrane.
The life span of such a reverse osmosis water purification system is largely dependent on the efficiency of the semi-permeable membrane. Over a period of time, the membrane's efficiency decreases due to adsorption of impurities on the membrane surface. Moreover, uncontrolled microbiological growth in a feed fluid tank, pipelines or on the membranes themselves can result in severe biofouling of the semi-permeable membrane. If this situation is detected in time, the membranes can be cleaned, for example by mechanical or chemical treatment processes. However, a major problem associated with this type of technology is the lack of methodology by which fouling or biofouling of the membrane is detected and monitored. If the membrane is not cleaned in time, the membrane can be damaged permanently, unavoidably resulting in downtime of the system, associated production losses, and expensive maintenance and replacement costs for replacing the membrane.
Apparatus have been developed in an attempt to detect fouling of the semi-permeable membrane in time, but these all suffer from one or more disadvantages. One such apparatus provides for monitoring fouling of the membrane, and hence performance of a reverse osmosis water purification system, by comparing electrical conductivity of an impure aqueous solution at an inlet side of the membrane with that of a substantially purified aqueous solution at an outlet side of the membrane.
Another known apparatus involves utilizing a centrifugal pump for increasing fluid pressure of a feed fluid to a value exceeding that of its osmotic pressure. Fouling of the semi-permeable membrane and performance of the water purification system is then monitored by means of three monitoring devices; one device for monitoring performance of the centrifugal pump; another for monitoring performance of a reverse osmosis apparatus incorporated in the system; and yet a further device for monitoring performance of fluid channels within the system. The monitoring devices generally determine respective pressure losses of fluid flow through the three apparatus and then compare the same with ideal operating conditions.
Yet a further apparatus provides for monitoring fluid pressure at an outlet end of the semi-permeable membrane and defining a correlation between a drop in such fluid pressure over a period of time, and the associated extent of fouling of the membrane.
It is apparent that most existing apparatus for detecting fouling of the semi-permeable membrane depend mainly on changes in fluid pressure or permeate flux of the membrane system. One disadvantage associated with these types of apparatus is that relatively complicated valve and pressure sensor arrangements are required to effect proper working of the apparatus. Another disadvantage is that the apparatus generally comprises a number of separate components that not only increases manufacturing, installation and maintenance costs, but also requires relatively skilled personnel for operating the apparatus. Furthermore, it has been found that existing apparatus are often not sensitive enough for detecting fouling of the membrane in time, the situation being such that by the time fouling is eventually detected, the membrane is already damaged.